Free-space photonic switching and computing systems utilize macroscopic optical elements such as holograms, gratings, lenses and mirrors as their basic hardware building blocks. In these systems, information is carried by arrays of beams of light which are collimated, manipulated and focused onto spatial light modulators in a stage-by-stage fashion. As such, free-space photonic switching systems provide the ability to interconnect a large number of communication channels at relatively high bit rates.
With respect to the design of lenses for a such free-space system, a number of requirements must be addressed. A lens is required to provide the focusing of a collimated beam array onto an array of light modulators. In order that each beam provide the correct "information", therefore, the light beams must be highly focused and distinct. In some cases, the beam arrays can be very large, on the order of a 64.times.64 element square. When the modulators utilized are symmetric self electro-effect devices (S-SEEDs), the switching speed is inversely proportion to the active window area of each S-SEED. Therefore, for relatively high rates of switching speed, relatively small active window areas are required. Thus, it is desired to minimize the f-number of the objective lens (to provide both a large numerical aperture and small spot size). Further requirements include diffraction-limited performance on a flat surface (essentially uniform illumination of the entire array) and telecentricity in the image space.
These and other requirements must therefore be considered when designing an objective lens for a free-space photonic switching system.